Energy

Efficient comminution strategies cut costs and energy consumption

By Elizabeth Lewis-Gray

Elizabeth Lewis GrayComminution is the single biggest electricity consumer on the mine site. It is both a major capital cost and a bottleneck for project development. In remote locations, supplying the required power for comminution means building major infrastructure in the form of power lines, pipelines and roads. More than half of the total energy used in the mining industry is for either crushing (18 per cent) or grinding (35 per cent). Grinding mills consume only five per cent of energy for reducing ore particle size; the remaining energy is wasted as heat and noise, and in destroying grinding media. This is hardly the most efficient use of what amounts to four per cent of all electricity consumed worldwide.

So can we do anything about it? Yes. There is plenty of room for improvement, and even incremental upgrades bring big benefits. By optimizing just three of their milling circuits, for instance, Barrick is saving 60,000 megawatt hours of power, or $5.2 million, each year.

Even larger gains will be made by looking at what, how and why we comminute with fresh eyes. If there is no mineral in a rock, why waste energy breaking it?

The following strategies may help companies developing projects in remote locations build smaller, less energy-intensive plants that require less infrastructure and are more ­efficient.

Advanced mine modelling: The mine model can be extended to show more than grade and to predict more than mining rates and costs. By including geometallurgical parameters, such as metal content, haul costs, recoverable grade, grinding index and liberation size, we can calculate the cost and the reward of processing, stockpiling or rejecting any parcel of ore. Different mine plans and cut-off grades can be tested to determine which overall strategy maximizes the economic return for the project,while minimizing energy use and the amount of infrastructure required.

Smart flowsheets – rejecting barren material before you grind it: Traditional flowsheets reduce the entire ore to the liberation size of the valuable mineral in one energy-intensive stream, while smart flowsheets concentrate on removing non-valuable material from the stream before the final size is reached. A smart flowsheet considers additional phases: pre-concentration, which targets valuable materials for separate treatment; gangue rejection, which targets barren material for removal; and pebble sorting, which removes coarse, hard-to-mill material.

Strategies for eco-efficient comminution

In many ore bodies, gangue surrounding valuable minerals are concentrated on mineral boundaries, so coarse material is often barren. New technologies and advanced designs have made coarse mineral separation more effective and efficient; these include optical and X-ray sorting, continuous gravity concentration and magnetic separation. The advantages of adopting new technologies extend beyond energy savings: one recent case study predicted a three per cent recovery increase on top of a 60 per cent energy consumption drop. Reduced operating costs also allow processing of lower grades, thus further increasing the recoverable resource and total project value.

If you are looking to reduce energy consumption during comminution, here are some features to look for in technologies you choose:

Smart blasting: improved explosives and blast patterns to produce a finer, more consistent process feed, and a better delineation between ore and waste.

Coarse flotation and continuous gravity ­separation: coarser grind size is made possible by advances to flotation and separation processes.

New crushing and grinding technologies: high-pressure grinding rolls, vertical shaft impactors and other technologies yield finer crush sizes, liberating minerals along grain boundaries and improving the effectiveness of separation techniques. The finer crush sizes allow for the use of more energy-efficient mills, like stirred mills, Isa mills and Plasma mills downstream.

More crushing, less grinding: a finer crush allows the use of more energy-efficient milling systems, as described above.

To learn more about how CEEC promotes new comminution strategies, visit www.ceecthefuture.org.


Author
Elizabeth Lewis-Gray is the chair of the Coalition for Eco Efficient Comminution (CEEC) and co-founder of Gekko Systems. CEEC is a not-for-profit entity established by industry to promote the sharing of ideas and research with the objective of facilitating the move to a more energy-efficient, economically rewarding future.

Post a comment

Comments

PDF Version